The present invention relates to a semi-aqueous cleaning formulation for use in producing semiconductor devices and a process for producing semiconductor devices using the cleaning formulation. More particularly, the present invention relates to a semi-aqueous cleaning formulation useful for cleaning organic materials, organometallic residues, organosilicon residues, sidewall polymers and inorganic residues from a semiconductor substrate.
The process of wafer fabrication includes a series of putting down layers. Each layer involves a series of steps, which may comprise all or some of photolithography, etch, strip, diffusion, ion implant, deposition, and chemical mechanical polishing.
Photolithography is the process through which images are transferred to the surface of a wafer by means of a light sensitive polymeric film layer (photoresist). The image is transferred from a mask to the photoresist layer by a developing process, which includes exposing regions of the film to a light/UV source, which are not blocked by the mask, resulting in a pattern on the wafer.
FIGS. 1(a)-1(d) depict four key photolithographic steps for an exemplary photoresist process. In FIG. 1a, photoresist (10) is deposited on a silicon dioxide, dielectric, hard mask, etch stop, and/or barrier layer (12) on silicon substrate (14). A light source (16) (as indicated by the down ward facing arrows) exposes the resist (10) not blocked by mask (18). The exposed resist (20), (the areas where the down arrows penetrate the resist layer), is dissolved in a developing solution, leaving a resist pattern identical to the mask (18). FIG. 1(b) depicts the resist pattern (22) on silicon dioxide layer (12) after dissolution of the exposed resist. In FIG. 1(c), the silicon dioxide layer (12) is then put into a plasma etch process or wet etch process typically using a fluorinated compound to remove the oxide in areas not protected by resist (22), to create a patterned silicon dioxide layer of vias and/or trenches. At this point, the photoresist has served its useful purpose and must be removed by an ashing and/or wet stripping step. The resist must be entirely removed since it is an organic material, which, if left on the wafer surface, would cause defects.
The plasma etch process used to remove the silicon dioxide or other substrate material requires exposing the substrate surface to UV radiation. The radiation tends to cross link the photoresist material making it more difficult to remove in the subsequent ashing or wet stripping step.
Ashing is a general term used for a process, which includes removing a photoresist coating by exposing the photoresist-coated wafer to an oxygen or hydrogen plasma in order to burn the resist film from the substrate surface. Alternatively, wet stripping typically involves contacting the photoresist-covered substrate with a stripper solution consisting primarily of an organic solvent and an amine. Of the two, plasma ashing is the more popular method for removing photoresist because it is less susceptible to contamination, as the process is carried out in a vacuum. FIG. 1(d) shows a patterned silicon dioxide layer (12), on the silicon substrate (14) after plasma ashing removal of the photoresist layer having particles and residues (24) left behind from the ashing process.
Prior to trench or via fill, the wafer surface must be cleaned of particles and residues left behind from the plasma etch and resist removal processes. The deposits may vary, but will most likely include at least an etching gas component, a component of the film being patterned by etching, and photoresist. If left in place, the deposits would cause a significant deterioration in the reliability of the semiconductor device. Accordingly, the wafer surface must be sufficiently cleaned of such deposits.
As fabs work to integrate new materials such as copper, and low dielectric constant materials, a need emerges for new cleaning techniques for post etch and post ash residue removal, where long trenches and narrow vias trap particles. Integration of low-dielectric constant materials with k less than 3.0 with existing aluminum or new copper damascene processes has been difficult to overcome.
Low-dielectric constant films such as carbon-doped oxide (OSG) comprise Sixe2x80x94O, Sixe2x80x94H and Sixe2x80x94C linkages. The film structure is preferably porous, whereby the porous nature of the film is due to the loss of volatile organic species or the inherent structure of the precursor material(s). In the presence of highly acidic or alkaline aqueous formulations, the Sixe2x80x94O and Sixe2x80x94H links are converted to OH groups, destroying the integrity of the Sixe2x80x94O link and increasing the dielectric of the low-k film.
One useful carbon-doped oxide (OSG) is a low-k material having a dielectric constant in the range of 2.7-3.0. The trend to single wafer tools for photoresist removal and post plasma/ash residual removal has mandated a short cleaning time to maintain wafer throughput. At the same time the introduction of organosilica glass (OSG) dielectrics has made the alkaline strippers and post-ash residual removers less viable since they attack OSG. The solution to high cleaning rate and compatibility with OSG requires new chemistries, which are formulated in such a way as to clean and remove particles without corroding the substrate surface.
Prior art cleaning formulations including highly-acidic, hydrofluoric acid are effective when the wafer substrate is made of a material, such as silicon, silicon dioxide, tungsten, tungsten-titanium alloys or titanium nitride. Such materials are relatively resistant to corrosion by a hydrofluoric acid. However, when made of materials, such as aluminum, aluminum alloys containing copper, copper or carbon-doped oxide, which are relatively less resistant to corrosion by the fluorine compound, the cleaning agent significantly corrodes and dissolves the conductive line pattern and/or dielectric.
Other prior art cleaning formulations have used alkanolamines to remove resist residues. However, if water is present during use, the alkanolamine dissociates and creates an alkaline solution that accelerates the corrosion of metals and dielectrics.
Other prior art cleaning formulations used organic solvents, which are no longer compatible with the new low-k dielectrics as they react with the organic and hydrogen substituents to produce a chemically altered dielectric material.
Hence, there is a need for an improved cleaning formulation that removes organic materials, organometallic residues, organosilicon residues, sidewall polymers and inorganic residues from a semiconductor wafer surface and inside and around via holes when low dielectric constant films and conductive lines containing aluminum and/or copper are exposed to plasma etch and resist ash conditions.
Further, there is a need for a cleaning formulation that is not effected by small changes in the concentration of acidic and/or basic components.
Therefore, it is one object of the present invention to provide an improved cleaning formulation that removes organic materials, organometallic residues, organosilicon residues, sidewall polymers and inorganic residues from a semiconductor wafer surface when low dielectric constant films and conductive lines containing aluminum and/or copper are exposed to plasma etch and resist ash conditions
It is a further object of the present invention to produce a cleaning formulation having a pH in a range that does not corrode metal and/or dielectric films and that is not effected by small changes in the concentration of acidic and or basic components.
A still further object of the present invention is to provide a cleaning agent for use in producing semiconductor devices, which meets the above objects.
A still further object of the present invention is to provide a process for producing semiconductor devices, which comprises a step of cleaning a wafer surface with a cleaning formulation that removes organic materials, organometallic residues, organosilicon residues, sidewall polymers and inorganic residues from a semiconductor wafer surface when low dielectric constant films and conductive lines containing aluminum and/or copper are exposed to plasma etch and resist ash conditions.
The present invention relates to a semi-aqueous cleaning formulation for semiconductor devices comprising a buffering system, and a low temperature process for cleaning a semiconductor substrate using the semi-aqueous formulation.
In one aspect, the present invention relates to a semi aqueous cleaning formulation comprising a buffering system.
In a further aspect, the present invention relates to a semi-aqueous cleaning formulation comprising a buffering system, a fluoride salt and a polar organic solvent and water.
In a still further aspect the present invention relates to a method of removing particles from a semiconductor substrate which includes, providing a semi-aqueous cleaning formulation comprising a buffering system and contacting the wafer surface with the cleaning formulation for a time sufficient to effect the removal of at least of portion of the particles.